Debug: The Half-Written Transfer

Transfer inserts a debit row and a credit row. A downstream constraint failure (set CjDb.FailOnInsertNumber = 2 in the test) means the SECOND insert can fail — and the buggy version leaves the debit visible: a half-written ledger. Fix: wrap BOTH inserts in a transaction (BeginTransaction ... CommitTransaction) so the write is all-or-nothing: on failure, NOTHING is committed; on success, both rows land. ``csharp static void Transfer(CjDb db, string from, string to); // CjDb: BeginTransaction(), CommitTransaction(), PendingTransactions property ``